“Hello, I know you!” Merle Haggard says as he emerges from the bedroom of his tour bus. He’s talking to Willie Nelson, who’s sitting in the bus’s cramped front quarters. Standing nearby, Nelson’s wife, Annie, asks the pair if they’ll sign a couple of acoustic guitars for a charity run by Matthew McConaughey, a friend of the family. “Absolutely not,” Haggard says with a smile. Later, when Annie takes a photo of the two signing the guitars, Nelson grins and gives the camera the finger.

It’s a perfect Saturday night in South Texas, where Haggard, 78, and Nelson, 82, are playing the last of three sold-out shows together at New Braunfels’ Whitewater Amphitheater. Haggard is about to play a set, during which Nelson will join him on “Okie From Muskogee,” “Pancho and Lefty” and a handful of other songs. Backstage, Nelson family members catch up; his rail-thin 90-year-old roadie Ben Dorcy (who was once John Wayne’s assistant) ambles around, smoking a pipe. Directly behind the stage, locals ride down the Guadalupe River in inner tubes, stopping on the bank to listen to the show. “We’ll get somebody out there to sell them tickets,” Nelson jokes.

Sitting side by side on the bus, Nelson and Haggard look like they could be a grizzled Mount Rushmore of country music. “It’s a mutual-admiration society with us,” says Nelson. “Merle’s one of the best. There’s not anyone out there that can beat him. Maybe Kris Kristofferson. But then you start running out of names.”

Haggard and Nelson are about to release a new LP, Django and Jimmie. (The title is a tribute to Nelson’s and Haggard’s respective heroes, Django Reinhardt and Jimmie Rodgers.)

One of the best songs is “Missing Ol’ Johnny Cash,” an ode to their late friend and a meditation on mortality. “There’s a thousand good stories about John,” says Nelson. Haggard tells one, about the time Cash thought it would be hilarious to dynamite a broken-down car he encountered on the side of the road. “He hooks it all up, hits the plunger and blows it up. And he said, ‘Now, when that guy goes to tell his old lady his car blew up, he won’t be lying!’?” Nelson cackles, adding, “John used to say, ‘I always get my best thinking done when June is talking.’?”

Nelson and Haggard met at a poker game at Nelson’s Nashville house in 1964, when both were struggling songwriters. (Neither would have major success until they left Nashville behind; Nelson for Austin, Haggard for Bakersfield, California.) They didn’t become close until the late Seventies, when they were playing casinos in Reno. “We’d play a couple of long shows a day, then spend all night long jamming,” says Haggard.

In 1982, they recorded Pancho & Lefty together at Nelson’s ranch near Austin, where they’d stay awake for days — “We were living pretty hard in that time period,” Nelson has said — playing golf and then recording all night (Haggard barely remembers singing his famous verse on “Pancho and Lefty”). At the time, they were fasting on a master-cleanse regimen of cayenne pepper and lemon juice. “I think Willie went 10 days,” says Haggard. “I went seven.”

These days, they share a love of conspiracy theories (both are devoted fans of paranormal-obsessed radio host Art Bell) and making music with their children (Haggard’s son Ben plays guitar in his band; Nelson’s sons Lukas and Micah frequently join their father onstage). “It’s as good as it gets, to have your kids up there playing,” says Nelson. “And they’re good!”

On the new album, the two cover Bob Dylan’s “Don’t Think Twice (It’s Alright).” The track was recorded before Dylan criticized Haggard and other artists in a widely publicized MusicCares speech in February: “Merle Haggard didn’t think much of my songs, but Buck Owens did,” Dylan said. “Buck Owens and Merle Haggard? If you have to have somebody’s blessing — you figure it out.” Dylan later apologized.

Haggard (who toured with Dylan in 2005) thinks Dylan was talking about the Merle Haggard of the Sixties — the guy who took shots at hippies, weed and premarital sex in 1969’s “Okie From Muskogee.”

“I didn’t misunderstand Bob,” says Haggard. “I know what he meant. He figured I was lumping him in with hippies [in the Sixties]. The lack of respect for the American military hurt my feelings at the time. But I never lumped Bob Dylan in with the hippies. What made him great was the fact that every body liked him. And I’ll tell you one thing, the goddamn hippies have got no exclusive on Bob Dylan!” He pauses. “Bob likes to box — I’d like to get in the ring with his ass, and give him somebody to hit.”

In fact, these days Merle Haggard is far more liberal than the man in his classic songs. For one thing, he loves pot. “I didn’t know anything about marijuana back then,” he says. “It’s one of the most fantastic things in the world.” Did he and Nelson smoke in the studio? “Are you kidding me?” Haggard says with a laugh.

Soon, the conversation devolves to jokes. “You know what you call a guitar player without a girlfriend?” Nelson asks. “Homeless.”

Next, they talk current events, Nelson explaining the “Blurred Lines” lawsuit to Haggard. (“They stole more than they were supposed to,” he says. Haggard nods.) Asked if either has any thoughts about communicating with fans through social media, they shake their heads. “Just so long as somebody else can do it,” says Nelson. “That’s why I didn’t learn to play steel guitar.”

“What was that little girl that played steel in Asleep at the Wheel?” says Haggard. “Cindy Cashdollar. Everybody was trying to look up her dress.”

“Oh, I wouldn’t do that,” deadpans Nelson. “I think I had the wrong angle.”

By now, Haggard is supposed to be onstage; his son has been extending his three-song warm-up set for several minutes, telling the crowd his father will be out soon. These co-headline dates sold so well that Nelson says there will be more: “In fact, I was talking to some folks today — I was gonna see what they thought of making us do a tour of it when it comes out.”

He turns to Haggard. “We ought to do whatever we can get — as many days as we need to,” Nelson says with a smile. “Because I know it’s a good record. I think it might sell a couple.”